This work is intended to locate the stem cells of the glycogen body, a structure composed of glycogen-filled cells in the lumbosacral region of the spinal cord of birds. The function of this unique structure is not understood. Future experiments aimed at learning the function of the glycogen body would be better directed perhaps if the embryological origin of the tissue was known. Since the lumbosacral nerve tube forms by primary neurulation of the neural folds, and by secondary neurulation from cells of the tail bud, one may ask whether the glycogen body takes origin from that part of the neural tube derived by primary neurulation or from the secondary neurulation of the tail bud. Experiments are proposed to transplant portions of the presumptive lumbosacral regions and tail buds of chick embryos 60-72 hours in age (when primary and secondary neurulation is taking place) to the chorioallantoic membranes of host chick embryos where the stem cells, if present, would differentiate as grafts of glycogen body. Grafts would be fixed, processed and sectioned in paraffin and in plastic for study with light microscopy. The presence of glycogen would be detected with periodic acid and Schiff's reagent for polysaccharides using diastase as a control for glycogen. Other experiments will test whether the tail bud contributes cells to the glycogen body. These involve tail bud extirpation, and homiotopic transplantation of quail tail bud to chick. Glycogen body would be detected histochemically, and quail cells, if present in glycogen body tissue of quail-chick chimaera would be detected by Feulgen staining of their nucleolar DNA.